The archival record makes clear that killing large numbers of civilians was the primary purpose of the atomic bombing of Hiroshima; destruction of military targets and war industry was a secondary goal and one that “legitimized” the intentional destruction of a city in the minds of some participants. The atomic bomb was detonated over the center of Hiroshima. More than 70,000 men, women, and children were killed immediately; the munitions factories on the periphery of the city were left largely unscathed. Such a nuclear attack would be illegal today. It would violate three major requirements of the law of armed conflict codified in Additional Protocol I of the Geneva Conventions: the principles of distinction, proportionality, and precaution. There could be great pressure to use nuclear weapons in future scenarios in which many American soldiers’ lives are at risk and there is no guarantee that a future US president would follow the law of armed conflict. That is why the United States needs senior military officers who fully understand the law and demand compliance and presidents who care about law and justice in war.